Well the 35% off only applies to those specific games. The 25% applies to [most] everything else. But no, you cannot stack vouchers, like ever. If something has a pre-existing standard discount, maybe 10% off for pre-orders or whatever, you usually can stack a single voucher on top of that. Exceptions would be stuff like XCOM, where they had a mandate of no vouchers allowed for North American users on that product. (That's why they came up with the store credit or cashback thing, and have been applying it unfairly/willy-nilly to other games since then...)

Starting this weekend and running for one week, we’re offering a 35% discount on some of the biggest hits of the last two months: The amazing turn-based strategy game XCOM: Enemy Unknown, everyone’s favorite Loot-Em-Up, Borderlands 2, and medieval decapitation simulator, Chivalry.

The voucher will be live from 1 PM UTC Saturday using this code at checkout: